The invention relates to fluid-operated apparatus or systems which can be utilized in motor vehicles, for example, to actuate or operate one or more consumers of pressurized fluid such as a torque transmitting unit (e.g., a friction clutch or a hydrokinetic torque converter with a bypass or lockup clutch), a transmission (e.g., an infinitely variable transmission with adjustable sheaves or pulleys and an endless flexible element trained around them), one or more cylinder and piston units, and/or others.
More particularly, the invention relates to improvements in fluid-operated systems of the type wherein one or more pumps and/or other suitable machines or units serve to pressurize a hydraulic or pneumatic fluid and the thus pressurized fluid is conveyed along one or more paths which lead toward one or more consumers or users or processors of pressurized fluid and wherein the pressure of fluid is or can be regulated, e.g., reduced, to assume an optimum value for utilization by or in the consumer or consumers.
It is often advisable or desirable to actuate (partly or fully engage or disengage) a friction clutch in the power train of a motor vehicle by resorting to a fluid-operated actor which can actuate the clutch in response to one or more signals transmitted by one or more switches, sensors, circuits and/or other monitoring devices serving to generate signals which denote certain variables or parameters such as the RPM of the engine, the selected gear of the transmission, the extent of depression of the gas pedal, the application or lack of application of one or more brakes and/or others. If the fluid-operated consumer is a clutch, it is necessary to ensure satisfactory operation of the clutch within a wide or even very wide range of torques which the clutch is called upon to transmit, e.g., from the rotary output element of an internal combustion engine or another suitable prime mover to the rotary input element of the transmission in the power train of the motor vehicle.
As a rule, a motor vehicle is operated in such a way that the clutch must transmit torque within a lower range of torques. However, the clutch should also be capable of operating satisfactorily when the torque being transmitted by the prime mover to the clutch is well in excess of the range of average engine torques, i.e., when the clutch is to transmit torque well in excess of a torque within the aforementioned lower range. It has been found that the lower range normally constitutes a greater (and often by far the major part) of the entire gamut of clutch torques between zero and a maximum value. It has also been ascertained that, in the case of single-stage systems which operate with a pressurized fluid and employ a regulating valve in the path for the flow of a pressurized fluid from the fluid pressurizing unit(s) to the consumer(s) of pressurized fluid, one can achieve or at least approach a required or an acceptable resolution or sensitivity or accuracy of adjustment or regulation within the entire operating range in spite of fluctuations or variations of the frequency of operation within certain sections or regions of the operating range. However, there still remains room for pronounced improvements which are desirable to enhance the comfort to the occupant(s) of the motor vehicle and contribute to smoother and more convenient operation or manipulation of the vehicle.